Shuttle-type transportation or conveying systems have been employed in which two passenger or load carrier units are coupled in a loop-type haul rope and driven back and forth between terminals, usually located proximate the ends of the haul rope loop. Such systems may or may not include intermediate terminals, and the passenger carrier units may be supported by wheels on a support surface or track, or suspended from the haul rope by means of support sheaves over part or all of the path.
A constant problem in such shuttle tramway systems is maintaining uniform, and preferably symmetrical tensioning forces in the haul rope. This is usually accomplished at the haul rope drive or bull wheels or through a counterweight assembly acting on the haul rope. Counterweight systems result in rope tension forces which are not always symmetrical in terms of the direction of driving of the haul rope, and bull wheel tensioning systems require complex carriage mounting assemblies.
Another difficult problem in connection with shuttle tramway systems is the problem of accurate docking at the terminals. Federal handicap access regulations require, for example, that there be no more than a one inch gap between the passenger carrier unit and the terminal at the ingress and egress doors for systems having a maximum speed of 20 miles per hour and not more than a three inch gap for systems having a maximum speed over 20 miles per hour.
In haul rope-driven conveying systems, the bull wheel which drives the haul rope can only be slowed and stopped with a certain degree of precision. It is desirable to accelerate the carrier units from zero to their maximum velocity and then decelerate them back down to zero at rates which are comfortable to passengers. The mass of the carrier units and their load (which will vary), however, will cause elastic stretching and even oscillation of the haul rope during the docking process and can produce slippage of the haul rope with respect to the driving bull wheel. Thus, over time, the combination of bull wheel imprecision, haul rope elasticity and carrier unit mass will create unacceptable docking imprecision, which in turn requires system adjustments. The problem is further complicated when two passenger carrier units are driven by a single haul rope in a shuttle system at which the passenger carrier units must dock simultaneously at opposed end terminals.
Haul rope tensioning devices have been employed in conveying systems which are mounted to the system carrier unit. U.S. Pat. No. 3,437,315, for example, shows a turn buckle-type tensioning assembly which is resiliently coupled between ends of a haul rope and the load carrying unit. This system, however, has no provision for sensing haul rope tension, much less automatically responding thereto to adjust rope tension. The haul rope adjustment assembly of this patent also is unpowered and must be manually adjusted. Russian Patent No. 614,007 shows a similar manually adjustable rope tensioning assembly.
In Swiss Patent No. 629,712 a device is shown for docking carrier units in a shuttle-type conveying system. The docking assembly docks one of two cars at a terminal and then reels or draws in the haul rope to dock the second car. This system, however, is not used to control haul rope tension. Other docking assemblies which do not control haul rope tension are shown in U.S. Pat. Nos. 3,875,868, 3,113,767 and 1,273,059, as well as French Patent No. 1,431,664 and Russian Patent No. 1,733,308.
Automatically maintaining the tension in traction members, and particularly metallic haul ropes, within prescribed limits, for example, 12,000 to 15,000 pounds, is also important and difficult to achieve. For example, the haul rope will predictably stretch during the first month of operation. Moreover, temperature changes can significantly effect the metal haul rope length. In a 1,000 foot long shuttle installation and a temperature difference of 56.degree. F. will produce a rope length change of 4.3 inches, which can cause, or combine with heavy loading to cause rope slipping on the bull wheels or undesirably high stress on the rope drive, particularly the drive output shaft. The tensioning problems are less severe in belt-type traction members because they usually operate at much lower tension forces.
In various urban environments, for example, at airports, considerable use of shuttle conveying systems has been made. Most of these systems, however, tend to be based upon a single car or passenger carrier unit that is railmounted and driven by a motor carried by the car or by driven tires adjacent to the car along the path to be travelled. Very little has been done with traction member-driven passenger conveying systems in urban applications.
Accordingly, it is an object of the present invention to provide a tensioning apparatus and method for a traction member-driven automated people mover transportation system which automatically adjusts haul rope tension on an as needed basis and allows symmetrical rope tension to be achieved regardless of the direction of haul rope advancement.
It is another object of the present invention to provide a haul rope-driven, load carrying, conveying or transportation system having a docking assembly which is capable of precise, repeated docking of the load carrying units or vehicles at terminals.
Still another object of the present invention is to provide a haul rope-driven passenger conveying system suitable for use in urban environments and having improved tensioning and docking capability.
Still a further object of the present invention is to provide a shuttle-type passenger conveying system which is durable, has a minimum number of components, can be easily repaired and maintained, and does not require an on-board operator.
The conveying system of the present invention and method have other features and advantages which will become apparent from and are set forth in more detail in the following description of the Best Mode Of Carrying Out The Invention.